U.S. Pat. No. 4,413,054 to Sprague dated Mar. 6, 1979 discloses 7-oxabicycloheptane and 7-oxabicycloheptene prostaglandin analogs which are prepared by the following methods.
In a first method maleic anhydride is made to react with an unsubstituted or substituted furan of the formula ##STR3## to form a compound of the formula ##STR4## which is reduced to form ##STR5## The above compound is then further reduced to form ##STR6## Treatment of the above compound with diisobutylaluminum hydride or diisobutylborane yields ##STR7## Submitting compound A to Wittig reaction conditions produces ##STR8## Compound C is then acylated and then hydrolyzed to form the aldehyde ##STR9##
All of the above compounds are in the form of racemic mixtures.
Aldehyde D is subjected to a Wittig reaction to form a compound of the structure ##STR10## which is esterified to form the corresponding lower alkyl ester. The hydroxymethyl group in the 3-position of the ester is then oxidized to obtain the aldehyde ##STR11##
Aldehyde F which is in the form of a racemic mixture is employed to form 7-oxabicycloheptane prostaglandin analogs.